This invention relates to a device for providing a circuit with resistive and capacitive characteristics wherein the resistive characteristic is controllable by electromagnetic radiation. The invention is particularly advantageous for providing a light dischargeable capacitor.
In many electrical instruments it is desirable to provide capacitors which can be discharged remotely without making electrical contact. Electrometers are used to measure current from current sources. Typically, an electrometer includes a capacitor which is charged by a current from the current source. After the current is measured, the capacitor in the electrometer must be discharged so that the electrometer can be used for measuring other current sources. In order to discharge the capacitor, the conventional method is by mechanical switching. Mechanical switching is disadvantageous, however, since electrical contacts in the mechanical switches may breakdown after repeated usage and that mechanical switches may be costly. It is therefore desirable to provide a capacitor which can be discharged without electrical contacts. It may also be desirable to provide capacitors which can be discharged remotely since capacitors may be placed at locations that are difficult to reach.
In certain applications, it may be desirable to provide a device equivalent to a capacitor placed in parallel to a resistor where the resistance of the resistor can be optically controlled.